代码 

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->unit UPeople;

interface

type
  TPeople = class(TObject)
  
  private
    _name:string; //私成成员定义
    procedure Set_Name(value:string);//Name属性的set方法定义
    function Get_Name:string; //Name属性的get方法定义

  protected
    function Get_Sex:Boolean;virtual;abstract; //定义抽象虚方法，由子类去实现
    
  public
    property Name:string read Get_Name write Set_Name; //定义Name属性
    property Sex:Boolean read Get_Sex; //定义Sex只读属性(该属性并未实现，而是交由子类去实现)
    class function ToString:string; //类方法，有点象c#中的static静态方法 
    procedure ShowName;//公用实例方法    
end;

//实现部分
implementation

    procedure TPeople.Set_Name(value:string);
    begin
      _name := value;
    end;

    function TPeople.Get_Name:string;
    begin
      result := _name;
    end;

    class function TPeople.ToString:string;
    begin
      result :=  'This is a People Class';
    end;

    procedure TPeople.ShowName;
    begin
      Writeln('姓名:' + _name);
    end;    
end.

代码 

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->unit UMan;
   
interface

uses
     UPeople ;
   
type
  TMan = class(TPeople)

  constructor Create(name:string); overload ; //重载构造函数

  
  private
    _sex:Boolean;

  protected
    function Get_Sex:Boolean; override;


  public
    function ToString:string; //实例方法

  end;

implementation

  constructor TMan.Create(name:string); //注意写法：实现的时候不用加overload关键字
  begin
     inherited Create;
     _sex := true; //男性强制定义为true
     Self.Name := name;
     
  end;

  function TMan.Get_Sex:Boolean;
  begin
    result := _sex;
  end;

  function TMan.ToString:string;
  begin
    result := '这是TMan中的ToString方法';
  end;

    
end.

代码 

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->unit UWoman;

interface

uses
     UPeople,UICook;
   
type
  TWoman = class(TPeople,ICook)

  constructor Create(name:string); overload ;

  
  private
    _sex:Boolean;

  protected
    function Get_Sex:Boolean; override;

  public
    procedure Cook;//接口的方法实现定义
    procedure ShowName;overload;

    //如果Class是从TObject继承的，又想实现接口的话，必须实现下面这三个function，
    //如果想偷懒的话，把UPeople改成从TInterfacedObject继承就可以省掉这个步骤了
    function _AddRef:Integer; stdcall;
    function _Release:Integer;stdcall;
    function QueryInterface(const IID:TGUID;out Obj):HResult; stdcall;
  end;

implementation

  function TWoman._AddRef:Integer;
  begin
      result :=-1;
  end;

  function TWoman._Release:Integer;
  begin
      result :=-1;
  end;

  function TWoman.QueryInterface(const IID:TGUID;out Obj):HResult;
  const
      E_NOINTERFACE = $80004002;
  begin
      if   GetInterface(IID,Obj) then
          Result := 0
      else
          Result := -1; {E_NOINTERFACE}
  end;   

  
  constructor TWoman.Create(name:string);
  begin
     inherited Create;
     _sex := false;
     Self.Name := name;     
  end;

  function TWoman.Get_Sex:Boolean;
  begin
    result := _sex;
  end;

  procedure TWoman.ShowName;
  begin
    Writeln('女人总是喜欢搞点花样，所以重载一下哈.')
  end;

  procedure TWoman.Cook;
  begin
    Writeln('因为我实现了ICook接口，所以我会做饭:)')
  end;

end.

代码 

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->unit UICook;

interface

type
  ICook = interface //定义一个接口
  procedure Cook;//接口的方法定义 
  end;

implementation

end.

代码

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->program ClassDemo;

{$APPTYPE CONSOLE}

uses
  SysUtils,
  UPeople in 'UPeople.pas',
  UMan in 'UMan.pas',
  UWoman in 'UWoman.pas',
  UICook in 'UICook.pas';

var
  aPeople:TPeople;
  aMan:TMan;
  aWoman:TWoman;
  aCook:ICook;

begin
  aPeople := TPeople.Create;
  aPeople.Name := 'jimmy.yang';
  Writeln(aPeople.Name);
  Writeln(TPeople.ToString);//调用静态方法
  aPeople.ShowName;

  Writeln('----------------------------------------');
  
  aMan := TMan.Create('杨俊明');
  Writeln(aMan.Name);
  Writeln(aMan.Sex);
  aMan.ShowName; //通过继承得来的方法
  Writeln(aMan.ToString);//TMan实例中的对象方法

  Writeln('----------------------------------------');

  aWoman := TWoman.Create('小龙女');
  Writeln(aWoman.Name);
  Writeln(aWoman.Sex);
  aWoman.ShowName; //调用重载后的方法
  aWoman.Cook;//实现接口得来的方法   
  Writeln('----------------------------------------');
  aCook := ICook(aWoman);//类还可以转化为接口
  aPeople.Free;
  aPeople:= TWoman.Create('翠花'); //同样也允许子类创建得到父类
  aPeople.ShowName;
  aWoman.Free;
  aWoman := TWoman(aPeople);
  aWoman.Cook;
  Readln;
end.